Dyeing of Silk Using Vegetable Dyes and Study on the Effects of Mordants on the Dyeing Properties

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Dyeing of Silk Fabric Using Vegetable Dyes and Study on the Effects of Mordants on

the Observed Dyeing Properties

Ahsanullah University of Science and Technology

By

Rakibul Islam Khan B. Sc. Tex. Tech.

Mohammad Abul Khair B. Sc. Tex. Tech.

Md. Mohidul Islam B. Sc. Tex. Tech.

Shariful Islam B. Sc. Tex. Tech.

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Acknowledgement

First of all, we would like to thank Almighty Allah for enabling us to finish the

project work successfully.

We would like to express our heartiest thanks to our project supervisor Mr. Mohammad Gias Uddin, Assistant Professor, Department of Textile Engineering, Ahsanullah University of Science & Technology (AUST) for his guidelines, valuable suggestions, constructive criticism and for providing all necessary supports. We are also grateful to our project co-supervisor Ms. Nahida Akter, Lecturer of the same department for her necessary advice and cordial supervision.

Special thanks to Professor Dr. Mustafizur Rahman, Head of Department of Textile Engineering, AUST for his continuous encouragement and co-operation in managing certain requisites of the project. Finally, we like to thank the respected teachers of our Department for their insights and suggestions.

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Table of Contents Chapter Title Page Abstract

1 Introduction 1-2 1.1 Objectives 3

2 Literature Review 4-5

2.1 History of Silk 6 2.2 Production of Silk 7-8 2.3 Chemical Composition of Silk 9 2.4 Types of Silk 10 2.5 Properties of Silk 11

2.5.1 Physical Properties 11 2.5.2 Chemical Properties 12 2.6 Pretreatment of Silk 13

2.6.1 Degumming of Silk 13 2.6.2 Bleaching of Silk 14 2.7 Vegetable Dyes 14

2.7.1 Henna (Lawsoniainermis) 14 2.7.2 Guava (Psidiumguajava) 15 2.7.3 Mango (Mangiferaindica) 16 2.7.4 Onion (Allium cepa) 17 2.7.5 Standardization of Dyestuff 18 2.8 Mordants 18

2.8.1 Alum 19 2.8.2 Iron (ferrous sulphate) 20 2.8.3 Tin (Stannous Chloride) 20 2.9 Chemistry of Natural Dyes 21 2.10 Colour Fastness 22

3 Materials and Methods 23

3.1 Materials 24 3.2 Chemicals 25 3.3 Tools and Machines 26 3.4 Pretreatment of Silk 27

3.4.1 Degumming 27 3.4.2 Bleaching 27 3.5 Dye Extraction 28

3.5.1 Dye Extraction from Leaves of Henna, Guava and Mango and from Onion Skins

28

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3.5.2 Selection of Dye Extraction Media 28 3.6 Mordanting 28

3.6.1 Pre-Mordanting 28 3.6.2 Post-Mordanting 28 3.6.3 Selection of Mordanting Method 29 3.7 Dyeing 29

3.7.1 Dyeing in Acidic Condition 29 3.7.2 Dyeing in Alkaline Condition 29 3.7.2 Selection of Dyeing Media 29 3.8 Colour Measurement 29

3.8.1 Transmittance % and Colour Strength 29-30 3.8.2 Reflectance and K/S values 31 3.8.3 Colour Co-ordinates 31 3.8.3 Colour difference, !cmc 32 3.9 Colour Fastness Methods 33

3.9.1 Dry Cleaning Fastness 33 3.9.2 Perspiration Fastness 33 3.9.3 Light Fastness 34 3.9.4 Wash Fastness 34 3.9.5 Rubbing Fastness 34 3.9.6 Evaluation of Change in Colour 34 3.9.7 Evaluation for Staining 35 3.9.8 Evaluation for Light Fastness 35

4 Results and Discussion 36

4.1 Selection of Extraction Media 37 4.2 Selection of Mordanting Method 38 4.3 Selection of Dyeing Media 39 4.4 Colour Measurements 39

4.4.1 % Reflectance and K/S Values 39-43 4.4.2 Colour Co-ordinates of the Samples 44-45 4.5 Fastness Results 46

4.5.1 Dry Cleaning Fastness 46-49 4.5.2 Perspiration Fastness 50-57 4.5.3 Light Fastness 58-60 4.5.4 Wash Fastness 61-63 4.5.5 Rubbing Fastness 64-66 4.6 Levelness of the Dyed Samples 67-70

5 Limitations and Suggestions 71-72 6 Conclusion 73-74 Appendix 75-76 Reference 77-78

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List of Tables

Table Name Page

2.1 World silk production in comparison with other textile fibres (Thousand tons)

7

2.2 Side groups in silk fibres 9 4.1 % Transmittance and colour strength% of different dye extraction condition 37 4.2 !cmc values of silk fabric using pre-mordanting and post-mordanting

technique 38

4.3 K/S value and wash fastness of silk fabric dyed under alkaline and acidic condition

39

4.4 Reflectance and K/S values of natural dyed silk fabric using various mordants

40

4.5 K/S values at various wavelength of the natural dyed silk fabric 41 4.6 The colour co-ordinates of silk fabric dyed with natural dyes using various

mordants 44

4.7 Dyed silk fabric samples 46 4.8 Dry cleaning fastness ratings of mordanted silk fabrics dyed with natural

dyes 47

4.9 Perspiration (alkaline) fastness ratings of mordanted silk fabric dyed with natural dyes

50

4.10 Perspiration (acidic) fastness ratings of mordanted silk fabric dyed with natural dyes

51

4.11 Light fastness ratings of mordanted silk fabrics dyed with natural dyes 58 4.12 Wash fastness ratings of mordanted silk fabrics dyed with natural dyes 61 4.13 Rubbing fastness ratings of mordanted silk fabrics dyed with natural dyes 64 4.14 Levelness data of silk fabric dyed with guava extract using various

mordants 67

4.15 Levelness data of silk fabric dyed with mango extract using various mordants

68

4.16 Levelness data of silk fabric dyed with onion extract using various mordants 69 4.17 Levelness data of silk fabric dyed with henna using various mordants 70

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List of Figures

Figure Name Page

2.1 Increment of silk production from year 1975 to 2010 8 2.2 Henna leaves 15 2.3 Lawsone [2-Hydroxy-1,4-naphthaquinone] 15 2.4 Guava 16

2.5 Quercetin [2-(3,4-dihydroxyphenyl)-3,5,7-trihydroxy-4H-chromen-4-one] 16

2.6 Mango 17

2.7 Mangiferin [2-beta-d-glucopyranosyl-1,3,6,7-tetrahydroxy-9h-xanthen-9-on] 17

2.8 Onion 17 2.9 Pelargonidin [2-(4-Hydroxyphenyl)chromenylium-3,5,7-triol] 18 2.10 Schematically presentation of three different mordanting strategies 19 2.11 Alum 20 2.12 Ferrous sulphate 20 2.13 Tin (Stannous Chloride) 21 2.14 Mechanism of pre-mordantation 21 2.15 Mechanism of post-mordantation 22 3.1 The L, a, b colour scale 31 3.2 Parameters of CMC colour discrimination ellipsoid 32 4.1 Formation of naphthaquinone salt in alkali solution 37

4.2 Aqueous extracts of henna, guava and mango leaves and onion skin extracted in alkaline condition 38

4.3 K/S values of the silk fabrics dyed with natural dyes using various mordants 40

4.4 K/S against Wavelength curve of silk fabric dyed with henna extract 42

4.5 K/S against Wavelength curve of silk fabric dyed with guava extract 42

4.6 K/S against Wavelength curve of silk fabric dyed with mango extract 43

4.7 K/S against Wavelength curve of silk fabric dyed with onion extract 43

4.8 Changes in L* of silk fabric dyed with natural dyes using various mordants 45

4.9 Dry cleaning fastness rating of silk fabric dyed with henna extract (Colour Change) 48

4.10 Dry cleaning fastness rating of silk fabric dyed with guava extract (Colour Change) 48

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4.11 Dry cleaning fastness rating of silk fabric dyed with mango extract (Colour Change) 49

4.12 Dry cleaning fastness rating of silk fabric dyed with onion extract (Colour Change) 49

4.13 Perspiration fastness rating of mordanted silk fabric dyed with henna extract (Colour Change) 52

4.14 Perspiration fastness rating of mordanted silk fabric dyed with guava extract (Colour Change) 52

4.15 Perspiration fastness rating of mordanted silk fabric dyed with mango extract (Colour Change) 53

4.16 Perspiration fastness rating of mordanted silk fabric dyed with onion extract (Colour Change) 53

4.17 Perspiration fastness rating of mordanted silk fabric dyed with henna extract (Staining of Wool) 54

4.18 Perspiration fastness rating of mordanted silk fabric dyed with guava extract (Staining of Wool) 54

4.19 Perspiration fastness rating of mordanted silk fabric dyed with mango extract (Staining of Wool) 55

4.20 Perspiration fastness rating of mordanted silk fabric dyed with onion extract (Staining of Wool) 55

4.21 Perspiration fastness rating of mordanted silk fabric dyed with henna extract (Staining of Cotton) 56

4.22 Perspiration fastness rating of mordanted silk fabric dyed with guava extract (Staining of Cotton) 56

4.23 Perspiration fastness rating of mordanted silk fabric dyed with mango extract (Staining of Cotton) 57

4.24 Perspiration fastness rating of mordanted silk fabric dyed with onion extract (Staining of Cotton) 57

4.25 Light fastness rating of mordanted silk fabric dyed with henna extract 59

4.26 Light fastness rating of mordanted silk fabric dyed with guava extract 59

4.27 Light fastness rating of mordanted silk fabric dyed with mango extract 60

4.28 Light fastness rating of mordanted silk fabric dyed with onion extract 60

4.29 Wash fastness rating of mordanted silk fabric dyed with henna extract (Colour Change) 62

4.30 Wash fastness rating of mordanted silk fabric dyed with guava extract (Colour Change) 62

4.31 Wash fastness rating of mordanted silk fabric dyed with mango extract (Colour Change) 63

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4.32 Wash fastness rating of mordanted silk fabric dyed with onion extract (Colour Change) 63

4.33 Rubbing fastness rating of mordanted silk fabric dyed with henna extract 65

4.34 Rubbing fastness rating of mordanted silk fabric dyed with guava extract 65

4.35 Rubbing fastness rating of mordanted silk fabric dyed with mango extract 66

4.36 Rubbing fastness rating of mordanted silk fabric dyed with onion extract 66 !

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Abstract

The main focus of the study was to analyze the dyeing properties of the mordanted silk

fabrics dyed with vegetable dyes. Degummed, bleached silk fabrics were mordanted with

chemical mordants and then dyed with the dyes extracted from mango, guava, henna

leaves and onion skins. The better results were obtained when dye extraction was carried

out in alkaline condition (pH 9) and dyeing in acidic medium (pH 5). The dyeing results

had been analytically assessed by measuring the K/S values of dyed samples using

reflectance spectrophotometer and by different fastness properties. CIE Lab co-ordinates

of the dyed silk had also been presented of the controlled and mordanted samples.

Different hues were obtained on silk fabric from the same dye extract by using different

mordants and their combinations. Better build up was obtained by using mordants

compared to dyeing without mordants. Deeper shades were obtained with ferrous

sulphate mordants whereas tin mordants produced lighter shades. The results of dry

cleaning, perspiration, light, wash and rubbing fastness tests were analytically assessed

for the dyed samples and comparative analysis was also done between dyeings with and

without mordants. Furthermore, fabrics that were dyed without using mordant were found

most evenly dyed. Use of ferrous sulphate mordant produced somewhat lesser even

dyeing.

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Chapter 1 Introduction

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The use of natural dyes for textile dyeing purposes, decreased to a large extent after the discovery of synthetic dyes in 1856. As a result, with a distinct lowering in synthetic dyestuff costs, the natural dyes were virtually unused at the beginning of twenties century [1]. Presently there is an excessive use of synthetic dyes, estimated at around 10,000,000 tons per annum, the production and application of which release huge amount of waste and unfixed colourants causing serious health hazards and disturbing the eco-balance of nature [2]. Today all over the world environmental regulations against control of effluents or hazards of synthetic dyes, are becoming more strict and are forcing the shift of technology towards less or non-polluting areas of technological development. The need to realize the importance and explore the technology of natural dyes is arguably more urgent.

Moreover, natural dyes produce very uncommon, specialty, soothing, and soft

shades as compared to synthetic dyes [3]. Worldwide the use of natural dyes for the colouration of textiles mainly has been confined to artisan/craftsman, small scale/cottage level dyers and printers as well as small-scale exporters and producers dealing with high-valued eco-friendly textile production and sales. These dyes exhibit better biodegradability and generally have higher compatibility with the environment. They are non-toxic, non-allergic to skin, non-carcinogenic, easily available and renewable [4]. In this sense natural dyes are more acceptable to the environmentally conscious people. Hence recently there has been revival of the growing interest on the application of natural dyes on natural fibres. In many of the worlds developing countries, natural dyes can offer not only rich and varied source of dyestuff, but also the possibility of an income through sustainable harvest and sale of these plants [4].

However, all natural colourants are not eco-friendly. There may be presence of

heavy metals or some other form of toxicity in natural dye. So, these colourants also need to be tested for toxicity before their use. But plant based vegetable dyes are eco-friendly in nature.

Nowadays, primarily natural colourants isolated from vegetable materials are used

as the potential dyestuff source. For this purpose, traditional dye plants have also been cultivated in many countries. As an estimate 1 kg of plant material will be required to dye 1 kg of textile goods [5], this indicates that the use of plant dyes available from different sources including secondary products will be competitive in cost to that of synthetic dyes.

Mango, henna and guava leaves as well as onion skins are good sources of natural

dyes. Mango trees are easily available in Rajshahi, Chapainawabganj, Nawabganj, and Dinajpur while in Barisal, Pirojpur, Jhalokathi and Chittagong guava trees are grown abundantly. Henna is also cultivated in Bangladesh and onions are widely used in Bangladesh cuisine, so onion skins can be easily found in abundance. As these are so readily available in Bangladesh, these can be used commercially for dyeing.

In this study colour extracted from leaves of mango, henna and guava and onion skin were carried out to dye silk fabric using alum, tin, iron and their combinations as mordants to focus the dyeing properties like colour co-ordinates, colour build up, fastness properties, levelness etc. In addition, silk fibre has good affinity towards natural dyes [6]. Therefore, silk fibre was chosen for this study.

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1.1 Objectives The main objectives of this study are:

1. To study the colour yield, colour co-ordinates and levelness of silk fabric dyed with natural colour extracted from henna, mango, guava leaves and onion skins.

2. To investigate the effects of various mordants such as alum, tin, iron and their combinations on the different dyeing properties of the natural dyed silk fabric.

3. Also to carry out the comparison of the silk fabrics between dyeings with and without mordants.

4. To determine %transmittance and colour strength of the natural dye extracted solution.

5. To analyze the colour fastness to dry cleaning, perspiration, light, wash and

rubbing of natural dyed silk fabric.

6. To develop the suitable extraction method as well as extraction medium of natural dyes.

7. To develop natural dyeing technology that can be applied in industrial and

domestic levels.

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Chapter 2 Literature Review

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The environment friendly dyes are enjoying resurgence in popularity as a result of concern with the carcinogenic, toxic and sensitizing characteristics of synthetic dyes. The ban on certain synthetic dyes has stimulated the entry of the golden era of natural dyes. Different literatures were studied regarding application of natural dyes on silk fabrics: Paul et al. (1996) in the article Natural dyes classification, extraction and fastness properties defined natural dyes as Dyes derived from natural resources. Natural dyes were classified based on chemical classes as, indigoid, anthraquinone, alpha-naphthoquinones, flavones, dihydropyrans, anthocyanidions and carotinoids. On the basis of color natural dyes were classified into red dyes, yellow dyes, blue dyes, black dyes, brown dyes, green dyes and orange dyes [7]. Singh (2000) studied on Natural dyes: The pros and cons, and defined natural dyes as a Colourant (dye or pigment) obtained from vegetable or animal matter without any chemical processing [8]. Almost any organic material will produce a colour when boiled in a dye-bath but only certain plants will yield a colour that will act as a dye. Natural dyes fall into following categories: Leaves and stems, barks, roots, outer skins, berries and seeds, insect dyes etc. (Padma S. Vankar, 2000) [6]. Frigerio (1992) compared characteristics of natural dyes with synthetic dyes to minimize environment pollution. Logwood, tropical legume dyes, yellow woad of Cuba, dyes extracted from insect, indigo, mollusks extraction and extraction from Sandalwood, saffron, henna and lichens are described [9]. Shaukat Ali (2007) in the article Evaluation of cotton dyeing with aqueous extracts of natural dyes from indigenous plants represented cotton fabric dyeing by using henna leaves, eucalyptus bark, and acacia bark, turmeric rhizomes where different extraction and dyeing procedures were maintained along with different mordant compositions. In the article it was shown that the alkaline conditions for extraction of dye from henna leaves were optimized and resulting extract was used to further optimize its dyeing conditions on cotton by exhaust method [10]. M. M Alam et al (2007) carried out Extraction of Henna Leaf Dye and its Dyeing Effects on Textile Fibre and found that the dye uptake by silk fibre was decreased with increase of dye concentration. Similarly the absorption of dye was increased with the decrease of dye concentration. The maximum dye absorption had been observed at 0.9% dye with 10% alum [11]. Guinot, et al (2007) investigated aqueous extracts of plant by-products (Onion, carrot, sage, spinach and thyme) for dyeing capacity on fibres. Light fastness of onion, thyme and sage samples, evaluated following a normalized test, was very promising considering industrial restrictions [12].

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Zin Mar Win & Moe Moe Swe (2008) carried out Purification of the Natural Dyestuff extracted from Mango Bark for the application on Protein fibres and found purified natural dyestuff extracted from mango bark gives subtle and soft colour to yarn [13]. Padma S Vankar et al (2009) in the article Dyeing of cotton, wool and silk with extract of allium cepa showed that pretreatment with 2% metal mordant and usage of 5% onion skin extract on silk had satisfactory fastness properties [14]. 2.1 History of Silk

Silk was first discovered in China about 5000 years back. As such China is called the "Birth place" of silk. At that time Ho Yang Ti was the Emperor of China. It is said that Emperor's 14 years aged Princess, one day taking tea in the orchard within the Palace. At that moment a silk cocoon was fallen in her cup. When she was trying to pick up that unknown thing she found that a delicate fibre had been coming out of it. The incident was thought to be the gift of God by the members of the Palace. The matter was kept secret within the four- walls of the palace for a long 2000 years.

In 140 B.C. silk spread from Tibet to Sub-Himalayan region of India. Afterwards, it spread different parts of India. In ancient time Arabian merchants used to export silk goods through 'Silk Road'. It was the longest land rout that extended from China to Greece of 10 thousand Kilometers.

Silk was introduced in Europe in 550 A.D. At that time, two Saints carried the technique of silk-culture from China to Constantinople. In 12th century, silk was introduced in Italy. From there it slowly expanded to France and Spain in 13th Century. In 4th Century, it was smuggled to Japan secretly. In1872, silk industry was considered the main industry in Japan. Afterwards, silk production was declined in Japan because of high labor cost, cultivable land pressure and industrialization. Recently a major thrush has been given in Russia and Brazil for more silk production.

In16th and 17th century during the Mughal regime there was abundant silk production in India. In Nawab regime there was tremendous progress of silk production in the undivided Bengal. In 1914, during the then British regime a separate department was established for silk development. In 1934, a Tariff Board was formed which made a good number of recommendations for the protection of the silk industry.

Sericulture in Bangladesh has a long history and glory. It inherits the same tradition of India. In 1947, after the partition of India two sericulture nurseries situated in Mirgonj (Rajshahi) and Bogra and some silk growing areas of Bholahat (Chapai-nawabgonj) and Mirgonj were fallen in the part of the then East Pakistan (now Bangladesh). Afterwards a massive sericulture development program had been under taken. Under those program 10 sericulture nurseries, one silk pilot project, silk-cum-lac research and training institute at Rajshahi were established in the country. In 1971 Bangladesh emerged as an independent country. From 1947 to 1977 Sericulture activities

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were looked after by organizations like Directorate of Industries and BSCIC. With a view to expand sericulture throughout the country a separate organization "Bangladesh Sericulture Board (BSB)" started functioning from February, 1978 with its Headquarters at Rajshahi - the Silk City [15]. 2.2 Production of Silk Fibre

Asia is the main producer of silk in the world and produces over 95 per cent of the total global output. Though there are over 40 countries on the world map of silk, bulk of it is produced in China and India followed by Japan, Brazil & Korea. China is the leading supplier of silk to the world with an annual production of 153942 MT (2006). India is the second largest producer of silk with 18475 MT (2006-07) and also the largest consumer of silk in the world.

For most silk producing countries, silk production is non-mechanized and family based. Production increases are therefore slow. Thailand and India fabrics are woven on hand looms, however power looms are increasing in India. Almost, all silk weaving is done on power looms in Vietnam, Brazil and Korea.

Silk has a miniscule percentage of the global textile fibre marketless than 0.2%. This figure, however, is misleading, since the actual trading value of silk and silk products is much more impressive. Silk is a multibillion-dollar trade; with a unit price for raw silk roughly twenty times that of raw cotton.

Worldwide silk production totals about a hundred thousand tones while the other natural fibres (cotton, wool) and synthetic fibres (nylon etc.) total in the tens of millions of tones. Being a natural product and relatively rare enables silk to maintain its value, however it must also have characteristics that create a demand. Any synthetic fibre has not duplicated the characteristics of these, but even if they are in the future, the natural product will remain in demand while there is consumer preference for natural over synthetic.

Though silk production is only about 0.2% of the total textile fibre production in the world, the production of silk together with other natural fibres doubled in the 20 years from 1975 to 1995, the production of synthetic fibres increased three fold [16].

Table 2.1: World silk production in comparison with other textile fibres

(Thousand tons)

Year Synthetics Cotton Other cellulose Wool Silk Total % Silk of

total production

1975 7346 11809 2959 1502 49 23665 0.21 1985 12151 17540 2999 1672 59 34786 0.17 1995 20200 19200 3000 1600 100 44100 0.23 2005 27850 23000 3125 1680 175 55830 0.32 2010 30050 26200 3180 1705 235 61370 0.38

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Figure 2.1: Increment of silk production from year 1975 to 2010.

Bangladesh has no position in the world silk market as it produces only 40 MT of raw silk per year. Interestingly the production of raw silk remains more or less same over the years. The low amount of raw silk production may be attributed to scattered small scale farming of mulberry plantation and silkworm rearing. Due to small amount of cocoon production in different places no reeling industry has yet been established in the country.

Only a few reeling units have so far been in operation in some places most of which are not fit for good quality raw silk production. As such the silk industries, mostly located in Rajshahi, have to depend on imported raw silk for fabric production. The extension activities of sericulture in Bangladesh are conducted at small-scale level, which is limited only with the landless and marginal farmers. It is mainly based on tree mulberry leaves except for Bholahat area under Chapai-nawabganj district where bush mulberry is cultivated for silkworm rearing. Most of the reapers of Bangladesh are landless poor and have no separate silkworm rearing houses of their own and as such they have to rear the silkworms in their dwelling houses where hygienic environment cannot be maintained for successful cocoon crop production. As a result sometimes silkworm diseases occur and cocoon production is greatly hampered.

Whenever Bangladesh Sericulture Board (BSB) gets fund through development projects they provide mulberry saplings to the farmers for plantation in the road and embankment sides. They also provide silkworm eggs to those farmers when planted mulberry trees become productive. But when the project period is over the extension activities are greatly hampered due to fund constrained as the next project sometimes gets approval after 2 -3 years. Again they have to start with new plantation of mulberry.

BSB has so far implemented 16 development projects during the period of 33 years since its inception in 1978. But it could not able to increase a tangible amount of

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100!150!200!250!

1975! 1985! 1995! 2005! 2010!Silk%Produ

ction%%%(Th

ousand

s%tons)%

Year%

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raw silk production in the country. This is mainly due to lack of proper extension policy and cocoon production planning. The sericulture projects implemented by BSB were more or less similar and routine in nature, which did not help develop sericulture in the country.

To meet the local demand we have to produce about 300 MT of raw silk per year. BSB should continue the program without any interval to meet the remaining demand of raw silk. BSB need to develop Package of sericulture practices for small, medium and large scale farming with the technical assistance of Bangladesh Sericulture Research and Training Institute (BSRTI). Then draw attention to the interested farmers and enterprises for implementation of the programs [15]. 2.3 Chemical Composition of Silk

Silk is a natural protein fibre, some forms of which can be woven into textiles. A variety of silks, produced by caterpillars and mulberry silkworm, have been known and used in China, South Asia, and Europe since ancient times. The strands of raw silk as they are unwound from the cocoon consist of the two silk filaments mixed with sericin and other materials. About 75 % of the strand is silk i.e. fibroin and 23 % is sericin; the remaining materials consist of fat and wax (1.5 %) and mineral salts (0.5 %). As a natural protein fibre silk has a significant attraction towards natural dyes.

Silk are formed by the polymerization of amino acids (with the general formula

NH2CHRCOOH) by means of peptide links (CONH) to give long-chain molecules with the general formula

R1, R2 represents the side groups present in the silk structure. Table 2.2 below shows the side groups present in silk fibres [17].

Table 2.2: Side groups in silk fibres Type Side group Amino Acid g amino acid per 100g of protein in silk

Neutral -H Glycine 43.80 Neutral -CH3 Alanine 26.4 Acidic -CH2COOH Aspartic acid 3.00 Acidic -CH2CH2COOH Glutamic acid 2.03 Basic -CH2. CH2.CH2. CH2.NH2 Lysine 0.88 Basic -CH2CN.CH.CH.NH2 Histidine 0.47

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2.4 Types of Silk [18] 2.4.1 Raw silk:

Silk fibre as it comes from the cocoon is coated with a protective layer called silk

gum, or sericin. The silk gum is dull and stiff. Silk with all of its gum is termed raw silk. 2.4.2 Tussah silk:

Silk made from wild silkworms is called tussah silk. The natural color of tussah

silk is usually not white, but shades of pale beige, brown and grey. It is usually coarser than cultivated silk. 2.4.3 Bombyxmori silk:

It is also known as mulberry silk which is produced by domesticated silkworm

raised on diet of mulberry leaves almost exclusively softer, finer and more lustrous than tussah silk. This silk produces shades of white product. 2.4.4 Reeled silk or Thrown silk:

It is term for silk fibre that is unwound from the silkworm cocoon. It is the most

fine silk, the fibres are very long, shiny and of great strength. 2.4.5 Spun silk:

Silk made from broken cocoon (from which the moths have already emerged) and short fibres, feels more like cotton. 2.4.6 Weighted silk:

When yarns are prepared for weaving, the skeins of yarn are boiled in a soap solution to remove the natural silk gum or sericin. The silk may lose from 20 to 30 percent of its original weight as a result of boiling. As silk has a great affinity for metallic salts such as those of tin and iron, the loss of weight is replaced through the absorption of metals. Thus a heavier fabric can be made at a lower price than that of pure silk, which is known as weighted silk. 2.4.7 Pure silk:

If the natural gum or sericin is removed from the silk and no further material is added to increase the weight of the fibre, i.e. silk containing no metallic weighting is called pure silk. Pure silk is exclusively soft and possesses fine luster.

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2.5 Properties of Silk 2.5.1 Physical Properties [18] 2.5.1.1 Tenacity - The silk filament is strong. This strength is due to its linear, beta configuration polymers and very crystalline polymer system. These two factors permit many more hydrogen bonds to be formed in a much more regular manner. Silk loses strength on wetting. This is due to water molecules hydrolyzing a significant number of hydrogen bonds and in the process weakening the silk polymer. 2.5.1.2 Specific gravity - Degummed silk is less dense than cotton, flax, rayon or wool. It has a specific gravity of 1.25.Silk fibres are often weighted by allowing filaments to absorb heavy metallic salts; this increases the density of the material and increases its draping property. 2.5.1.3 Elastic-plastic nature - Silk is considered to be more plastic than elastic because its very crystalline polymer system does not permit the amount of polymer movement which could occur in a more amorphous system. Hence, if the silk material is stretched excessively, the silk polymers that are already in a stretched state (They have a beta-configuration) will slide past each other. The process of stretching ruptures a significant number of hydrogen bonds. 2.5.1.4 Elongation - Silk fibre has an elongation at break of 20-25% under normal condition. At 100% R.H. the extension at break is 33%. 2.5.15 Hygroscopic nature - Because silk has a very crystalline polymer system, it is less absorbent than wool but it is more absorbent than cotton. The greater crystallinity of silk's polymer system allows fewer water molecules to enter than do the amorphous polymer system of wool. It absorbs water well (M.R.11%), but it dries fairly quickly. 2.5.1.6 Thermal properties - Silk is more sensitive to heat than wool. This is considered to be partly due to the lack of any covalent cross links in the polymer system of silk, compared with the disulphide bonds which occur in the polymer system of wool. The existing peptide bonds, salt linkages and hydrogen bonds of the silk polymer system tend to break down once the temperature exceeds 1000C. 2.5.1.7 Electrical properties - Silk is a poor conductor of electricity and tends to form static charge when it is handled. This causes difficulties during processing, particularly in dry atmosphere. 2.5.1.8 Hand feel - The handle of the silk is described as a medium and its very crystalline polymer system imparts a certain amount of stiffness to the filaments. This is often misinterpreted, in that the handle is regarded as a soft, because of the smooth, even and regular surface of silk filaments. 2.5.1.9 Drapes Property - Silk fibre is flexible enough and if silk fibre is used to make

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garments, then the fabric drapes well and this is why it can be tailored well too. 2.5.1.10 Abrasion resistance - Silk fabric possess good abrasion resistance as well as resistance to pilling. 2.5.1.11 Effect of sunlight - Silk is more sensitive light than any other natural fibre. Prolonged exposure to sunlight can cause partially spotted color change. Yellowing of silk fibre is generally occurred due to photo degradation by the action of UV radiation of sunlight. The mechanism of degradation is due to the breaking of hydrogen bonds followed by the oxidation and the eventual hydrolytic fission of the polypeptide chains. 2.5.2 Chemical Properties [18] 2.5.2.1 Action of water - The absorption of water molecules takes place in the amorphous regions of the fibre, where the water molecules compete with the free active side groups in the polymer system to form cross links with the fibroin chains. As a result, loosening of the total infrastructure takes place accompanied by a decrease in the force required to rupture the fibre and increase extensibility. Treatment of silk in boiling water for a short period of time does not cause any detrimental effect on the properties of silk fibre. But on prolonged boiling, silk fibre tends to loss its strength to some degree, which thought to occur because of hydrolysis action of water. Silk fibre withstands, however, the effect of boiling better than wool. 2.5.2.2 Effect of acids - Silk is degraded more readily by acids than wool. Concentrated sulfuric and hydrochloric acids, especially when hot, cause hydrolysis of peptide linkages and readily dissolve silk. Nitric acid turns the color of silk into yellow. Dilute organic acids show little effect on silk fibre at room temperature, but when concentrated, the dissolution of fibroin may take place. On treating of silk with formic acid of concentrated about 90% for a few minutes, a swelling and contraction of silk fibre occur. Like wool, silk is also amphoteric substance, which possesses the ability to appear as a function of the pH value either as an acid or as a base. 2.5.2.3 Effect of alkalis - Alkaline solutions cause the silk filament to swell. This is due to partial separation of the silk polymers by the molecules of alkali. Salt linkages, hydrogen bonds and Van der Waals' forces hold the polymer system of silk together. Since these inter-polymer forces of attraction are all hydrolyzed by the alkali, dissolution of the silk filament occurs readily in the alkaline solution. Initially this dissolution means only a separation of the silk polymers from each other. However, prolonged exposure would result in peptide bond hydrolysis, resulting in a polymer degradation and complete destruction of the silk polymer. Whatever, silk can be treated with a 16-18% solution of sodium hydroxide at low temperature to produce crepe effects in mixed fabric containing cotton. Caustic soda, when it is hot and strong, dissolves the silk fibre. 2.5.2.4 Action of oxidizing agent - Silk fibre is highly sensitive to oxidizing agents. The attack of oxidizing agents may take place in three possible points of the protein-

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1. At the peptide bonds of adjacent amino groups, 2. At the N-terminal residues and 3. At the side chains

Though fibroin is not severely affected by hydrogen peroxide solution, nevertheless may suffer from the reduction of nitrogen and tyrosine content of silk indicate that hydrogen peroxide may cause breakage of peptide bonds at the tyrosine residues resulting in the weight loss of the fibre. The action of chlorine solution on the silk fibroin is more harmful than does the solution of hypochlorite. These solutions, even at their lower concentration, cause damage to fibroin. 2.5.2.5 Action of reducing agents - The action of reducing agents on silk fibre is still a little bit obscure. It is, however, reported that the reducing agents that are commonly found in use in textile processing such as hydrosulfite, sulfurous acids and their salts do not exercise any destructive action on the silk fibre. 2.6 Pretreatment of Silk 2.6.1 Degumming of Silk [19]

The process of eliminating Gum (sericin) from raw silk is known as degumming of silk. Degumming of silk involves mainly the removal of sericin from the fibroin. Sericin is insoluble in water. It is comparatively easily hydrolyzed whereby the long protein molecule of sericin is broken down into smaller fractions, which are easily dispersed or solubilized in hot water. Hydrolysis of proteins can be carried out by treatment with acids, alkalis and enzymes. Acids are non-specific and tend to attack vigorously. Alkalis also attack both, sericin and fibroin. However, the variation in the rate of hydrolysis is large enough to control the reaction.

The degumming with soaps in the presence of mild alkalis like soda ash is practiced. Degumming with alkalis is a function of pH, temperature and duration of treatment. The pH should be kept at the leve1 of 9.5 to 10.5. If the level is below 9.5, then the process of removing sericin will be slow. If the pH is over 10.5, the weight loss will be greatly increased.

The degumming loss in this process is usually 20-25%. In certain cases, entire silk gum is not removed, but only sufficient amount is removed to make the silk soft and lustrous and workable in dyeing and bleaching. This is known as Soupling in which only 10% to 15 % of the gum is removed. In addition to removing the soil and additives used while weaving silk, scouring removes any sericin (gum) that remains on the silk. Often a quantity of the natural gum has been allowed to remain on the silk fibre to give it additional body and to make it easier to handle in spinning and weaving.

Although for raw silk fabrics the gum is retained purposely to provide body or produce a different texture, most silk fabrics are degummed as a part of the finishing process. The resultant fabric has a much softer hand and a whiter appearance. Raw silk is

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sometimes given a very mild scouring for the purpose of softening the fibre. This is called as "Ecru silk in which only 2 to 5% in weight of silk gum is removed. Ecru silk can be prepared by simply washing the raw silk in hot water without the use of soap. This is used mainly for warp; hence the gum is left purposely. 2.6.2 Bleaching of Silk [19]

The silk being spun by silkworm contains natural colouring matter tinted with yellow, yellow -green and brown pigments. During degumming the removal of sericin from the silk results in dull white to lightly tinted material. Since some of the sericin is closely held by fibroin, complete elimination of the colour by degumming is not possible. During bleaching these natural colouring matters are decolorized /removed to produce pure white material. An efficient bleaching process must ensure pure whiteness and level dyeing properties and non- degradation of the material. The bleaching of silk is based on the use of either reducing agents or oxidizing agents. Some of the important reducing agents used for bleaching are- a) Sodium hydrosulphite (Hydrose) b) Sulphur dioxide c) Sodium/Zinc sulphoxylate Formaldehyde

The above reducing agents at time tend to de-oxidize original colour may be restored in the bleached material. The popular oxidizing agents used for bleaching of silk are: a) Hydrogen peroxide b) Potassium permanganate c) Sodium perborate d) Sodium peroxide

The chlorine-based agents such as bleaching powder are not generally used, as they tend to chlorinate the silk fibroin. Hydrogen peroxide is most commonly used for bleaching. 2.7 Vegetable Dyes

Potential dye plants include trees, shrubs and herbs, as well as mushrooms and lichens. The plant components used for dyeing are also very different. It can be the whole plant (e.g. weld), the leaves (e.g. woad), the roots (e.g. madder), the flowers (e.g. dyers chamomile), the fruits (e.g. common buckthorn), the bark (e.g. oaks), the semen shell (e.g. Persian nut) or, the skin (e.g. onion) [5]. 2.7.1 Henna (Lawsonia inermis)

Lawsonia inermis is commonly known as henna. It is also called mehndi in native language in subcontinent (Bangladesh, India and Pakistan). Henna is a well-

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branched shrub or, small tree frequently cultivated in many tropical and warm temperature regions of Bangladesh, Pakistan, India, Egypt, Sudan, Iran, Yemen and Kenya. Large-scale cultivation for the sake of leaves that yield dye confined to India, Egypt, Pakistan, Bangladesh and Sudan. Powdered leaves of this plant (aqueous paste) are used as a cosmetic for staining hands and hairs. The picture of plant is given in Figure 2.2 [10].

Figure 2.2: Henna Leaves

Unbroken henna leaves will not stain hand, hair or textile materials. Henna's

colouring properties are due to lawsone, a burgundy organic compound that has an affinity for bonding with protein. Lawsone is primarily concentrated in the leaves, especially in the petioles of the leaf [10]. The structure of the coloring component, Lawsone, is given in Figure 2.3.

Figure 2.3: Lawsone

[2-Hydroxy-1,4-naphthaquinone] 2.7.2 Guava (Psidium guajava)

Guava (Psidium guajava) is a low evergreen tree or shrub 6 to 25 feet high, with

wide-spreading branches and square, downy twigs, is a native of tropical America. Guava is a tropical and semi-tropical plant [20]. It is well known for its edible fruit. Figure 2.4 shows guava fruit and its leaves.

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Figure 2.4: Guava

The leaves of guava contain many essential oils and so it is used for many

purposes like producing anti-microbial finishes, providing anti-diarrheal action, having anti-inflammatory effect, etc. The leaves can also be used for dyeing textiles. Quercetin present in the guava leaves is the chemical that is responsible for having the coloring effect on textile material [20]. The chemical structure of Quercetin is given in Figure 2.5.

Figure 2.5: Quercetin [2-(3,4-dihydroxyphenyl)-3,5,7-trihydroxy-4H-chromen-4-one]

2.7.3 Mango (Mangifera indica)

Mango (Mangifera indica) is one of the most popular of all tropical fruits. Mangoes belong to genus Mangifera, which consists of about 30 species of tropical fruiting trees in the flowering plant family Anacardiaceae. It is native tropical Asian fruit and has been cultivated in the Indian subcontinent for over 4000 years and is now found naturalized in most tropical countries [13]. The picture of mango tree is given in Figure 2.6.

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Figure 2.6: Mango

The chemical that is responsible for colour in the mango leaf is mangiferin. Figure

2.7 is the chemical structure of Mangoferin.

Figure 2.7: Mangiferin [2-beta-d-glucopyranosyl-1,3,6,7-tetrahydroxy-9h-xanthen-9-on]

2.7.4 Onion (Allium cepa)

The onion (Allium cepa) is also known as the bulb onion. Onions are often

chopped and used as an ingredient in various hearty warm dishes. Onion tissue is frequently used in science education for demonstrating microscope usage. Onion skins can also be used as dyes. The picture of onion is given in Figure 2.8.

Figure 2.8: Onions

The dyestuff present in onion skin is called Pelargonidin (3,5,7,4 tetrahydroxyantocyanidol) [21]. The structure of Pelargonidin is given in Figure 2.9.

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Figure 2.9: Pelargonidin [2-(4-Hydroxyphenyl) chromenylium-3,5,7-triol]

2.7.5 Standardization of the Dyestuff

Natural raw material shows variations of quality, dyestuff content and composition of the plant due to the effects of weather/climate, soil, fertilization, location, etc. Such materials can be used for handicraft dyeing where the uniqueness of a product is well advertised. In other words, the dyeing result alters depending on the crop as long as no product standardization has been performed to adjust plant materials to a fixed standard. For enlarged application of natural dyes in the textile industry a certain level of repeatability is required. Basically the standardization of agricultural material is more important than that of a secondary product, e.g. from the food industry. Especially in the food sector strict quality assurance of the final product (e.g. fruit juice) already results in constant constitution of the waste. Although this may facilitate the standardization an assessment of the dyeing properties and respectively dyestuff content is necessary. In general, information on the quality of plant material and related colouration features may be obtained from dyeing experiments. Unfortunately, extraction of natural dyestuffs and subsequent colouration requires a minimum of two hours of process time. Therefore, indicating parameters that will allow prediction of the later dyeing result would be essential [5]. 2.8 Mordants

Mordants are metal salts that can form metal complex with the natural colourants, which exhibit increased affinity to the substrate. Depending on the metal character the complex formation does not only strengthen dyestuff fixation on the substrate but also changes the colour of the dyeing. In some cases the resulting change in shade can be seen as an opportunity to steer colour in a wider range [5]. Some mordants will also change the hue of certain dyes (different mordants on the same dye may darken, brighten or drastically alter the colour-may be a desired effect as well as an unwanted phenomenon).

Basically, three different types of mordanting strategies can be distinguished: pre-, after and meta-mordanting. The processes mainly vary in the time of mordant addition. While pre- and after-mordanting require an additional treatment step in a separate bath (a

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mordant solution with defined concentration of the metal salt), the simple addition of a concentrated salt solution directly to the dye bath is used in the so-called meta-mordanting process. Generally small variations in the colour depth are found if the three mordanting types are compared. In most cases pre-mordanting leads to darker shades compared to meta-mordanting, as shown in the literature [5]. Figure 2.10 represents the three mordanting strategies schematically.

! Figure 2.10: Schematically presentation of three different mordanting strategies

Generally mordants that were used over time were divided into two types; acid and basic, where acid mordants are used to bond acid dyes and basic mordants to bond basic dyes. Acid mordants have generally been derived from tannin, readily available from oak balls or bark; occasionally they are vegetable oils. Basic mordants, however, come from the salts of various metals, particularly aluminium, chromium, iron, copper, zinc or tin [5]. Most of the vegetable dyes, however, require some sort of mordant to set permanently in any fibre. 2.8.1 Alum

The mordants used in Egypt in early Christian times included alum, but also salts of iron, such as the acetate, specially prepared from iron and vinegar, and the sulfate, which occurs frequently as an impurity in alum [5]. Alum is translucent crystalline water-soluble element, which has a pH of 3.2. It is also known as potassium aluminum sulphate. Alum attracts moisture and is used in textile processing as a dye fixative. A pinch of alum

!Type Step 1 Step 2 Number of

Baths

Pre mordanting

After mordanting

Meta mordanting

Mordanting

Dyeing

Dyeing

Mordanting

2

2

1 Mordant solution is added to dyeing bath !

!!Raw!Substrate!!!!Coloured Substrate

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makes colour flow but if too much is used it will make the fibre harsh and sticky. Alum is best suited to be used on wool and silk fibre. It is considered non-toxic and is for water treatment. Alum is also used for pickling fruits and vegetables and in baking process [22]. Alum salts as mordants intensify the obtained colour brilliance but do not influence the colour shade to the same extent as iron do [5].

Figure 2.11: Alum

2.8.2 Iron (Ferrous Sulphate)

Ferrous sulphate is grey-white to greenish crystalline powder that turns brown when exposed to air. When used as a dye mordant, iron darkens the dye colour. Especially the use of iron mordants leads to substantial colour differences and primarily results in a colour shift towards dark shades [5]. For this reason iron is also called the greying mordant. When too much iron is used it causes harsh and spotty fibre. This mordant is best suited for cellulosic fibre and silk. Iron is considered toxic only when it is ingested in large amounts. Iron can be removed from water by adding potassium permanganate and oxidizing it to form iron hydroxide. The hydroxide is a precipitate and can be easily removed by filtration [22].

Figure 2.12: Ferrous Sulphate

2.8.3 Tin (Stannous Chloride)

Stannous chlorides are white flakes having a characteristic odour and it clumps if air reaches it. Tin produces the brightest color compared to other available mordants, but it can damage the fibre and make it harsh and brittle. At very high temperatures, stannous chloride is very volatile. Therefore to avoid poisonous fumes, tin is usually added to water [22].

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Figure 4.13 Tin: (Stannous chloride)

2.9 Chemistry of Natural Dyes

The majority of natural dyes need a mordanting chemical (Preferably metal salt or suitably coordinating complex forming agents) to create an affinity between the fibre and dye or the pigment molecules of natural colorant. These metallic salts form metal complexes with the fibres and the dyes. After mordanting, the metal salts, anchored to the fibres, attracts the dye/organic pigment molecules to be anchored to the fibres and finally creates the bridging link between the dye molecules and the fibre by forming coordinating complexes [18].

Molecules of silk consist of amino acid units. Proteins are formed from amino acid, which contains free amino and carboxyl groups. Therefore, silk can be considered as amphoteric compounds. During dyeing of the silk, a hydrogen bond occurs between the dyestuff and amino groups.

There are three ways of mordanting, pre-mordanting, post-mordanting and meta-

mordanting.

Mechanism of pre-mordantation and post-mordantation of onion dye on silk fibre is shown in Figure 2.13 and Figure 2.14 respectively [21].

Silk ------------------ Mordent (Men+) ------- Dyestuff

Figure 2.14: Mechanism of pre-mordantation

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During pre-mordantation the mordant first bonds with amino and carboxyl groups in silk by covalent bonds and co-ordinate bonds and then the mordants bonds with the dyestuff by covalent bonds and co-ordinate bonds. This way the mordant creates a bridge between silk and dyestuff and thus causes fixation of the dyestuff to the silk fibre.

Silk ---------------------- Dyestuff--------------- Mordent (Men+)

Figure 2.15: Mechanism of post-mordantation

During post-mordantation the dyestuff first bonds with amino and carboxyl groups in silk by covalent bonds and co-ordinate bonds and then the dyestuff bonds with the mordant by covalent bonds and co-ordinate bonds. Here the mordants do not act as a bridge; instead the mordants block the active sites of the dye molecule so that it cannot react with other chemicals and become detached from the dye.

During meta-mordanting the dyestuff and mordants are added simultaneously

during dyeing. Both types of reactions as shown in Figure 2.13 and Figure 2.14 take place during meta-mordanting. 2.10 Colour Fastness

Fastness tests and the resulting staining are important tools for assessing the quality and the stability of dyeing. In many cases the fastness properties are strongly related to the substrate type and mordant used for dyestuff fixation. Besides the dyestuff itself there are many factors that influence the fastness, such as the substrate, the surrounding conditions (water, solvents, chemicals, temperature, humidity, light intensity and light source, etc.), pre- and after-treatments, as well as dyestuff distribution in the fibers/textile and also the amount of dyestuff fixed on the goods.

In natural dyeing color fastness of the natural dyes requires considerable attention

and careful selection of materials and processes. The colour fastness quantifies the colour change on a dyed material under specific conditions and also the transfer of dyestuff to uncoloured adjacent material (bleeding) [5].

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Chapter 3 Materials & Methods

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3.1 Materials 3.1.1 Fabric

Greige 100% silk fabric of plain construction EPI 132, PPI 132, warp count 22 denier and weft count 22 denier, was collected from Sopura Silk Mills Ltd. Dhanmondi, Dhaka, Bangladesh. 3.1.2 Leaves

Henna, guava and mango leaves were collected from Botanical Garden, Mirpur,

Dhaka. 3.1.3 Onion Skin

Onion skin was collected from Ahsanullah University of Science and Technology

(AUST) cafeteria. 3.1.4 Multi-fibre fabric

DW multi-fibre fabric (ISO 105 F10) with a construction of di-acetate, bleached

cotton, acrylic, polyamide, polyester and wool was collected from Overseas Marketing Corporation (Pvt.), Dhaka, Bangladesh. It was used in wash and perspiration fastness tests. 3.1.5 Cotton Twill Fabric

2/2 Twill Cotton fabrics were collected from Fabric Manufacturing Lab of AUST.

It was used in dry cleaning fastness test. 3.1.6 Filter Paper

Filter paper (Filter speed medium) was collected from WPT Lab of AUST. It was

used in dry cleaning fastness test as well as during filtration of extracted dyes. 3.1.7 Crocking Cloth

Crocking cloth of 100% cotton desized and bleached without optical brightener

having 1/1 plain construction and EPI 32and PPI 33 was collected from TTQC Lab of AUST. It was used in rubbing fastness test.

3.1.8 Wool Blue Standard

Wool blue standards of James H. Heal Co. Ltd, Halifax, England was collected

from WPT Lab of AUST. It was used during light fastness test.

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3.2 Chemicals 3.2.1 Mordants

Alum (potassium aluminium sulphate), iron (ferrous sulphate) and tin (stannous

chloride) were used as mordants. The chemicals were collected from M/S. R. Traders, Armanian Street, Bongshal, Dhaka, Bangladesh. 3.2.2 Standard Soap

Standard soap (OBA Free) from James H. Heal Co. Ltd, Halifax, England was

collected from WPT Lab of AUST. It was used during degumming of raw silk and during wash fastness test.

3.2.3 Sequestering agent

Dekol Dis SN of BASF, Germany was collected from WPT Lab of AUST.

3.2.4 Wetting agent Kieralon OL of BASF, Germany was collected from WPT Lab of AUST.

3.2.5 Hydrogen Peroxide (H2O2)

Hydrogen Peroxide (35%) of HP Chemicals Ltd. Bangladesh was collected from

WPT Lab of AUST. It was used for bleaching silk fabric. 3.2.6 Tri Sodium Phosphate

Tri Sodium Phosphate of MERCK, India was collected from WPT Lab of AUST.

It was used during bleaching of silk fabric. 3.2.7 Sodium Hydroxide

0.1 N Sodium Hydroxide of MERCK, India was collected from WPT Lab of

AUST. 3.2.8 Acetic Acid

100% Acetic Acid of MERCK, India was collected from WPT Lab of AUST.

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3.2.9 L-histadinemonohydrochloride monohydrate L-histadinemonohydrochloride monohydrate of LOBA CHEME, India was

collected from Wet Processing Lab of AUST. It was used for preparation of artificial perspiration solution. 3.2.10 Di-sodium hydrogen orthophosphate

Di-sodium hydrogen orthophosphate of LRG, Germany was collected from Wet

Processing Lab of AUST. It was used for preparation of artificial perspiration solution. 3.2.11 Perchloroethylene

Perchloroethylene of Russian commercial grade was collected from M/S. R.

Traders, Armanian Street, Dhaka, Bangladesh. It was use during dry cleaning fastness. 3.3 Tools and Machines 3.3.1 Dyeing machine

IR sample dyeing machine of Datacolor, AHIBA, USA was used for degumming,

bleaching, mordanting and dyeing of silk fabric.

3.3.2 Oven Dryer Oven dryer of Binder, Germany was used for drying collected leaves and for

perspiration fastness testing. 3.3.3 Gyrowash

Gyrowash of James H. Heal Co. Ltd., Halifax, England was used for wash

fastness testing and dry cleaning fastness testing.

3.3.4 Crockmeter Crockmeter of James H. Heal, Halifax, England was used for rubbing fastness

testing. 3.3.5 Microsol light fastness tester

Microsol light fastness tester of James H. Heal, Halifax, England was used for

light fastness testing.

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3.3.6 Grey scale for Assessing Colour Change Grey scale for assessing Colour Change (ISO 105-A02) was collected from WPT

Lab of AUST. 3.3.7 Grey scale for Assessing Staining

Grey scale for assessing Staining (ISO 105-A03) was collected from WPT Lab of

AUST. 3.3.8 Spectrophotometer and Colour Matching Software

Spectrophotometer and Colour matching software (Data Colour, USA) from

TTQC-II Lab of AUST were used for measuring colour values. 3.3.9 Miscellaneous

Electronic Balance Electric Heater Thermometer Dryer Pipette pH strip Beaker Measuring Cylinder Stirrer Steel Container (dye bath) Mortar

3.4 Pretreatment 3.4.1 Degumming

The raw silk fabric was degummed by treating with soap (15 g/l), sequestering agent (1 g/l) and wetting agent (1 g/l), maintaining a material and liquor ratio of 1:50 at pH 9 and temperature 80C for 60 minutes in the IR sample dyeing machine [23]. 3.4.2 Bleaching

The degummed silk fabric was bleached by treating with hydrogen peroxide (3

g/l), sequestering agent (1 g/l) and wetting agent (1 g/l), maintaining a material and liquor ratio of 1:50 at pH 10 and temperature 85C for 60 minutes. Tri-sodium phosphate was used as a stabilizer and the bleaching was carried out in IR sample dyeing machine [23].

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3.5 Dye Extraction 3.5.1 Dye extraction from henna, guava and mango leaves and from onion skin. 3.5.1.1 Alkaline Extraction: The leaves were first dried in the oven dryer and then grinded into powder using a mortar. The dye was then extracted from the powder or onion skin by boiling in water maintaining material and liquor ratio of 1:10 at pH 9 for 60 minutes. Sodium hydroxide was used to increase pH [10]. 3.5.1.2 Acidic Extraction: The leaves or skin were treated in similar way using acid bath at pH 5 for 60 minutes. Acetic acid was used to decrease pH.

3.5.1.3 Neutral Extraction: The leaves or skin were treated in similar way using pH 7 for 60 minutes. 3.5.2 Selection of Dye Extraction Media

Mango leaves were used for selection of dye extraction media. Known quantity of the mango leaves was soaked in water with material and liquor ratio 1:10. The pH was changed to acidic (pH 5) and alkaline (pH 9) by adding acetic acid and sodium hydroxide respectively for two baths. The dye was extracted by boiling the material for 60 minutes. In a third bath, extraction at pH 7 was carried out. The coloured dye extracts were then filtered and the transmittance% was found. In addition, the colour strength of dye extracted in alkaline condition and dye extracted in acidic condition were found by comparing the two with the dye extracted in neutral condition. 3.6 Mordanting Mordanting was done in two different ways. 3.6.1 Pre-Mordanting The silk fabrics were pretreated with the solution of different mordants (25% of the weight of fabric) maintaining material to liquor ratio 1:10 at 70C for 60 minutes in the dyeing machine. Then the pretreated silk fabric was introduced into the dye bath containing required amount of dye extract and water [24]. 3.6.2 Post-Mordanting In this method, samples were first dyed using the dye extract. Then the dye fabric was introduced in the bath containing the mordant. Material to liquor ratio of 1:10 was maintained. Mordanting was done at 70C for 60 minutes in the IR sample dyeing machine [24].

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3.6.3 Selection of Mordanting Method Mango extract was used in this case for the selection of suitable mordanting methods for dyeing of silk fabric. Pre-mordanting and post-mordanting methods were analyzed. Alum was used as the mordant here. The colour co-ordinates of the dyed samples were determined by spectrophotometer against the control sample (Fabric dyed without mordant). 3.7 Dyeing 3.7.1 Dyeing in Acidic Condition

Pre-mordanted silk fabric was dyed with the extracted dye solution, maintaining material and dye solution ratio of 1:30 at pH 5 and temperature 80C for 60 minutes in the dyeing machine. The dyed samples were taken out, squeezed, washed with water and dried at room temperature. Acetic acid was used to decrease pH [10]. 3.7.2 Dyeing in Alkaline Condition

Pre-mordanted silk fabric was dyed in the similar way at pH 9 and temperature 80C for 60 minutes in the dyeing machine. Sodium hydroxide was used to increase pH [10]. 3.7.3 Selection of Dyeing Media

Dyeing was carried out in acidic condition (pH 5) and in alkaline condition (pH 9) in separate baths using mango extract and alum mordant (25% o.w.f) using pre-mordanting method. Then K/S values and wash fastness of the silk fabric dyed in different conditions was analyzed using spectrophotometer. 3.8 Colour Measurement 3.8.1 % Transmittance and Colour strength The Lamberts Law states that the fraction of light absorbed by a substance is independent of the intensity of light and, in other words, layers of equal thickness of the same substance transmit the same fraction of incident light at a given wavelength irrespective of its intensity. The Beers Law refers to the effect of the concentration of the coloured substance on the absorption of light and states that the absorption of light is proportional to the number of absorbing molecules in its path, i.e. the concentration of the absorbing solution.

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The two laws may be combined and stated as follows. I = I!!!!!"# (eq. 1) Or, log !!! = !!"# (eq. 2) Here, I = intensity of transmitted light Io = intensity of incident light ! = molar extinction coefficient (litre/mole/cm)

c = concentration of the absorbing solute (mole/litre) L = path length or thickness of the absorbing layer, cm

Transmittance (T),

T = !!! = !!!"# (eq. 3) log!! = !!! = !"# = ! (eq. 4)

The optical density or absorbance, D has a linear relation with concentration up to a certain limit. The laws are valid only for monochromatic radiation and for non-scattering solution of very low concentration. Colour strength value is a numerical value related to the amount of colourant in a solution. It is often used to calculate the difference in strength % between two coloured solutions. The relative colour strength, S of two solutions may be given by

! = 100! !!!!!!!! (eq. 5) Where, C is the dye concentration.

Assuming equal concentration of the dyes (C1= C2), the equation can be simplified as equation 6.

! = 100! !!!! (eq. 6) Where the subscript 1 and 2 refer to the reference dye and dye under test respectively [25].

For selection of dye extraction media, transmittance % of the dye extracted in different condition was found using spectrophotometer. In addition, the colour strength of dye extracted in alkaline condition and dye extracted in acidic condition were found by comparing the two with dye extracted in neutral condition.

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3.8.2 Reflectance and K/S values

The reflectance and K/S values were determined for all the samples using KubelkaMunk equation (equation 7). The reflectance is the ratio of the light leaving an object versus the total light that was hitting the object and K/S is the determination of colorant strength from reflectance measurement [26]. The K/S value was calculated by the formula given below! !! = ! (!!!)!!! (eq. 7) R= reflectance of the coloured fabric K= absorption co-efficient S= scattering co-efficient The reflectance and K/S values were found using the spectrophotometer. 3.8.3 Colour Co-ordinates

The colour co-ordinates of the dyed samples were determined by spectrophotometer using colour-matching software (Data Colour international, USA) against the control sample (Fabric dyed without mordant) and the difference in co-ordinates DL*, Da* and Db* were calculated. The DL* values represents the difference in lightness of the colour, Da* value corresponds to the difference of colour position on the red-green axis and the Db* value is the difference of colour position on the yellow-blue axis. The total colour difference is expressed by ECIE .[27]. !CIE= !" ! + ! !" ! + !" ! (eq. 8) The Figure 3.1 shows the L, a, b colour scale

Figure 3.1: The L, a, b colour scale

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3.8.3 Colour Difference, !cmc

In 1984, the Colour Measurement Committee of the Society of Dyers and Colourists defined a colour difference measure based on the L*C*h colour model. Named after the developing committee, the value is called !cmc [26]. !cmc is a single number measurement that defines an elliptical colour difference space around the standard product.

The distance of a colour (L*2, C*2, h2) to a reference (L*1, C*1, h1) is !cmc= !2!!1!"! ! + ! !2!!1!"! ! + !!ab!! ! (eq. 9)

SL= 0.511!!!!!!!!!!!!!!!!1 < 16!.!"!#$%!!1!!!.!"#$%!!1 !!!!!!!!1! 16!!!!!!!!!!!! (eq. 10)

SC =

!.!"#$!1!!!.!"#"!1 + 0.638 (eq. 11) SH = Sc(Tf+1-f) (eq. 12)

f = !1!!1!!!"## (eq. 13)

T =0.56 + ! 0.2!cos!(1 + 168) 164 !1! 345!0.36 + ! 0.4!cos!(1 + 35) otherwise!!!!!!!!!!!!!!!!!! (eq. 14)

Here l and c are the relative lightness and chroma tolerances required for a

particular application. For perceptibility data l:c should be 1:1. For acceptability l:c should be 2:1, lightness difference is less significant. SL, SC and SH indicates the length of half-axes of the ellipsoid defining unit !around the standard (Std) as shown in figure 3.2.

Figure 3.2: Parameters of CMC colour discrimination ellipsoid

! !

33!

For gradual transition from neutral to saturated colours in treatment of half-axis SH, an addition function f is considered. f increases gradually as chroma increases. When f = 0, SH and SC are equal and difference in hue and chroma are considered to be equivalent. This corresponds to a uniform Cartesian coordinates. When f = 1, SH and SC are unequal and the equation corresponds to polar coordinate system with unequal radial and tangential discrimination [27].

For evaluating levelness, !cmc values were measured on four different places of the dyed fabric. One value was taken as standard and other values were considered as batch and mean values were calculated. 3.9 Colour Fastness Methods 3.9.1 Dry Cleaning Fastness

Dry cleaning fastness was carried out following ISO 105 D01 method where 10

cm by 4 cm dyed silk fabric and 12 steel balls were place inside a bag, which was prepared by sewing two 10 cm by 10 cm twill cotton fabric on three sides, and then treated in 200 ml of perchloroethylene at 30C for 30 minutes in a Gyrowash. The dyed silk fabric was assessed using grey scale for assessing color change (ISO 105-A02) and perchloroethylene was assessed using grey scale for assessing staining (ISO 105-A03) [28].

3.9.2 Perspiration Fastness

Perspiration fastness was carried out following ISO 105 E04 method where 10 cm

by 4 cm dyed silk fabric was sewed to a 10 cm by 4 cm DW multi-fibre fabric and then soaking in artificially prepared perspiration (acidic and alkaline) maintaining material and liquor ratio 1:50 for 30 minutes. Excess liquor was squeezed out such that the composite fabric weight was 2 to 2.5 times its original weight and then was placed between two glass plates under12.5 kPa (4.5 kg weight) pressure and the kept in oven dryer at 372 C for 4 hours. Then the dyed silk fabric was assessed using grey scale for assessing color change (ISO 105-A02) and DW multi-fibre fabric was assessed using grey scale for assessing staining (ISO 105-A03).

Alkaline perspiration was prepared artificially by adding 0.5 g L-histidinemonohydrochloride monohydrate, 5 g sodium chloride and 2.5 g disodium hydrogen orthophosphate dihydrate to 1 litre of water and then the pH was adjusted to 8 (0.2) using 0.1 mol/litre sodium hydroxide as required.

Acidic perspiration was prepared artificially by adding 0.5 g L-histidinemonohydrochloride monohydrate, 5 g sodium chloride and 2.2 g disodium hydrogen orthophosphate dihydrate to 1 litre of water and then the pH was adjusted to 5.5 (0.2) using acetic acid as required [29].

! !

34!

3.9.3 Light Fastness Light fastness was carried out following ISO 105 B02 method where 5 cm by 1

cm of dyed silk fabrics and 5 cm by 1 cm of blue wool reference standards were attached on 14 cm by 5 cm card boards and then the card boards were placed inside the Light fastness tester and it was exposed under mercury lamp for 36 hours. The fabrics were then evaluated by comparing with the wool blue standards [30]. 3.9.4 Wash Fastness

Wash fastness was carried out following ISO 105 C02 method where 10 cm by 4

cm dyed silk fabric was sewed to a 10 cm by 4 cm DW multi-fibre fabric. The composite fabric was then treated with a solution containing standard soap (5 g/l), maintaining material and liquor ratio of 1:50 at 50C for 45 minutes in a Gyrowash machine. Then the dyed silk fabric was assessed using grey scale for assessing colour change (ISO 105-A02) and DW multi-fibre fabric was assessed using grey scale for assessing staining (ISO 105-A03) [31]. 3.9.5 Rubbing Fastness

Rubbing fastness was carried out following ISO 105 X12 method where 5 cm by

14 cm of dyed silk fabric was placed in the Crock meter and then rubbed by 5 cm by 5 cm dry crocking cloth (For dry rubbing fastness) and then rubbed by 5 cm by 5 cm wet crocking cloth (For wet rubbing fastness) 10 strokes in 10 seconds. Then the crocking cloth was assessed using grey scale for assessing staining (ISO 105-A03) [10]. 3.9.6 Evaluation of Change in Colour

Original sample and tested specimen were placed adjacent to each other in the

same place and oriented in the same direction along with the respective grey scale. The visual difference between original and tested specimens in the presence of light at an angle of 45 was compared by viewing perpendicular to the plane of the surface with the grey scale for assessing colour change (ISO 105-A02) and assigned suitable colour fastness rating [26]. Ratings of colour change Grade 1- Very poor (great loss in depth) Grade 2- Poor (significant loss) Grade 3- Fair (Appreciable loss) Grade 4- Good (Slight loss in depth) Grade 5- Excellent (No change)

! !

35!

3.9.7 Evaluation for Staining Unstained samples and stained multi-fibre fabrics were placed adjacent to each

other in the same plane and oriented in the same direction along with the respective grey scale. The visual difference between unstained and stained sample in the presence of light at an angle of 45 was compared by viewing perpendicular to the plane of the surface with the grey scale for assessing staining (ISO 105-A03) and assigned suitable colour fastness rating. [26] Ratings for staining Grade 1- Very poor (Deep staining) Grade 2- Poor (Significant staining) Grade 3- Fair (Moderate staining) Grade 4- Good (Very slight staining) Grade 5- Excellent (No staining) 3.9.8 Evaluation for Light fastness The wool blue standards and the dyed fabrics that were exposed under light was placed adjacent to each other in the same plane and the similarities between the fabric and wool blue standards was observed in the presence of light at an angle of 45 by viewing perpendicular to the plane of the surface. The fabric light fastness rating was the rating of the wool blue standard with which the colour contrast of the fabric was similar. [26] Ratings for light fastness Grade 8- Outstanding (No fading) Grade 7- Excellent (Very slight fading) Grade 6- Very Good (Slight fading) Grade 5- Good (Moderate fading) Grade 4- Moderate (Appreciable fading) Grade 3- Fair (Significant fading) Grade 2- Poor (Extensive fading) Grade 1- Very Poor (Very extensive fading)

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Chapter 4

Results and Discussion

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4.1 Selection of Extraction Media

From the Table 4.1 it was observed that the transmittance% of dyes extracted in alkaline condition was less compared to dye extracted in acidic condition. Therefore from this result it can be said that more amount of dye was extracted in the bath liquor under alkaline condition compared to acidic and neutral condition.

Table 4.1: %Transmittance and colour strength% of different natural dye extraction

Veg. Dye pH Transmittance % Colour strength %

Alkaline 0.50 134.81 Henna

Leaves Neutral 1.00 -

Acidic 3.00 77.55

Alkaline 7.50 119.61 Guava Leaves Neutral 12.00 -

Acidic 33.50 46.06

Alkaline 5.00 168.40 Mango Leaves Neutral 20.00 -

Acidic 30.00 78.07

Alkaline 2.30 119.14 Onion Skins Neutral 4.20 -

Acidic 9.80 73.09

The reason can be attributed to acidic hydroxyl group in naphthaquinone, which reacts with alkali and form naphthaquinone salt (Figure 4.1), which is more soluble in water. Thus the extraction of colouring component becomes more in alkaline medium. Furthermore, as cell wall of leaves is made up of cellulose material, this gains anionic charge in alkaline medium. Due to these anionic repulsive forces around cell walls, it loses its strength and ruptures easily in alkaline medium. This gives more colouring component in alkaline medium [10].

Figure 4.1: Formation of naphthaquinone salt in alkali solution

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It was observed that the colour of the dye extracted from henna leaves, guava leaves and onion skins were dark brown while the dye extracted from mango leaves was of orange. The colour of the extract baths has been shown in Figure 4.2.

Figure 4.2: Aqueous extracts of henna, guava and mango leaves and onion skin extracted in alkaline condition 4.2 Selection of Mordanting Method

From the data found in Table 4.2, it was observed that the !cmc values of dyed pre-mordanted silk fabric were found around 0.20 with the lowest variation in different places of the fabric and in case of post-mordanting samples !cmc values were found comparatively more. Therefore the silk samples dyed using pre-mordanting technique was found more even compared to the samples dyed using post-mordanting technique.

Table 4.2: !cmc values of dyed silk fabric using pre-mordanting and post-mordanting methods

As the results of pre-mordanting were better than post-mordanting technique,

dyeings were done using pre-mordanting method. Again, the affinity between dyes and mordant were more compared to that of dyes and fibre. Therefore during post-mordanting, the mordant pulled out the dyes from the fibre, which resulted in uneven dyeing [10].

Veg. Dye Mordant Mordanting Methods DL* DC* DH* !cmc Mango Leaves Alum

Pre-mordanting

-0.24 -0.06 -0.01 0.25 -0.05 0.13 0.15 0.20 -0.05 0.07 0.16 0.19 -0.27 -0.09 -0.04 0.21

Post mordanting

1.07 0.81 0.54 1.44 1.10 0.84 0.57 1.47 1.07 0.69 0.54 1.40 1.05 0.79 0.52 1.42

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4.3 Selection of Dyeing Media It was observed from Table 4.3 that K/S value was found more when dyeing was

done under acidic condition in comparison to alkaline condition. Prolonged exposure of the silk fibre in alkaline condition caused degradation of the silk polymer. Therefore the dye take-up by the fibre was less under alkaline condition. Hence the colour yield (K/S) and wash fastness was found better under acidic condition. Table 4.3: K/S value and wash fastness of silk fabric dyed under alkaline and acidic

condition

Veg. Dye Mordant pH K/S

Colour change

Staining

Di-Acetate

Bleached Cotton Acrylic

Poly-amide Polyester Wool

Mango Leaves Alum

9 (alkaline) 12.91 2/3 5 4/5 5 5 5 3/4

5 (acidic) 16.58 4/5 5 4/5 5 5 5 4/5

It was observed that the wash fastness of silk fabric dyed in alkaline condition

was not satisfactory. Grey scale ratings for colour change were found good to excellent when dyed in acidic condition.

The silk fibre dyed in alkaline condition became damaged and could not form

bonds with the natural dyes and mordants adequately [18]. So the wash fastness was not found satisfactory in this condition. Therefore, natural dyeings were carried out on silk fabric using acidic condition.

4.4 Colour Measurements: 4.4.1 %Reflectance and K/S values From Table 4.4 it was found that for all the vegetable dyed silk fabrics maximum reflectance was achieved when dyeing was done without using any mordant. Hence the K/S values were found minimum when dyeing was done without using mordant. In all the cases, lowest reflectance% was obtained using ferrous sulphate mordant while alum and tin mordants increased the reflectance % comparatively. Hence corresponding K/S values for all the dyed samples were found regarding the reflectance data, which also formed a trend that K/S values decreased along with the increase of wavelengths as shown in Table 4.5 and Figure 4.4 to Figure 4.7.

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Table 4.4: Reflectance and K/S values of natural dyed silk fabric using various mordants

Veg. Dye Mordant Reflectance % (= 360 nm) K/S

(= 360 nm)

No mordant 4.00 12.94

Ferrous Sulphate 3.00 15.87

Ferrous Sulphate and Alum 3.00 17.11 Henna Ferrous Sulphate, Alum and Tin 3.50 17.12 Leaves Alum 3.00 16.01

Alum and Tin 3.50 17.78

Tin 3.50 16.03



Ferrous Sulphate and Alum 2.90 14.23 Guava Ferrous Sulphate, Alum and Tin 3.50 12.96 Leaves Alum 3.00 14.32


Tin 3.90 12.49



Ferrous Sulphate and Alum 2.50 17.13 Mango Ferrous Sulphate, Alum and Tin 3.00 15.20 Leaves Alum 3.00 14.86


Tin 4.00 14.37



Ferrous Sulphate and Alum 3.50 16.48 Onion Ferrous Sulphate, Alum and Tin 3.00 15.24 Skins Alum 3.50 16.36


Tin 4.00 14.08 Figure 4.3 showed the bar diagrams of K/S values of the vegetable dyes obtained from Table 4.4.

Figure 4.3: K/S values of the mordanted silk fabrics dyed with natural dyes

0!5!

10!15!20!

K/S%

Henna%Leaves%%%%%%%Guava%Leaves%%%%%%%%%Mango%Leaves%%%%%%%%Onion%Skin%%

Vegetable%Dye%

No!mordant!Ferrous!Sulphate!Ferrous!Sulphate!and!Alum!Ferrous!Sulphate,!Alum!and!Tin!Alum!Alum!and!Tin!Tin!

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Table 4.5: K/S values at various wavelengths of the natural dyed silk fabric

Veg. Dyes

Mordants

K/S

= 360nm

= 380nm

= 420nm

= 460nm

= 500nm

= 540nm

= 580nm

= 620nm

= 660nm

= 700nm

Henna Leaves

No mordant 12.94 9.87 4.06 3.08 2.49 1.71 1.11 0.86 0.71 0.55

Ferrous Sulphate 15.87 15.25 11.60 8.91 7.31 7.15 6.05 4.45 3.75 2.91

Ferrous Sulphate and Alum 17.11 15.97 10.96 7.56 5.89 4.31 4.28 3.69 1.94 1.59

Ferrous Sulphate, Alum and Tin 17.12 15.54 9.27 7.82 4.91 3.52 2.51 1.91 1.34 0.95

Alum 16.01 15.42 10.58 6.72 4.65 3.23 2.16 1.51 1.19 0.82

Alum and Tin 17.78 16.06 9.28 6.35 4.25 2.88 1.86 1.29 0.88 0.59

Tin 16.03 14.40 7.94 5.42 3.81 2.55 1.58 0.95 0.85 0.61

Guava Leaves

No mordant 12.45 11.68 3.64 2.25 1.79 1.21 0.89 0.71 0.39 0.29




Alum 14.32 13.57 4.91 1.95 1.38 0.96 0.75 0.62 0.51 0.45

Alum and Tin 13.00 12.27 2.81 1.39 0.91 0.71 0.59 0.31 0.38 0.21

Tin 12.49 11.45 2.28 1.19 0.79 0.59 0.51 0.38 0.31 0.29

Mango Leaves

No mordant 11.48 10.91 1.67 0.81 0.69 0.54 0.35 0.31 0.21 0.19




Alum 14.86 16.58 14.28 2.19 1.11 0.91 0.79 0.59 0.31 0.29

Alum and Tin 13.77 14.17 3.06 0.95 0.59 0.49 0.34 0.29 0.31 0.12

Tin 14.37 15.21 2.63 0.89 0.55 0.51 0.45 0.31 0.29 0.19

Onion Skin

No mordant 7.09 7.73 1.46 0.79 0.71 0.65 0.51 0.32 0.15 0.09




Alum 16.36 18.14 12.00 5.00 2.69 1.71 1.19 0.89 0.61 0.45

Alum and Tin 12.74 14.58 5.88 2.86 1.92 1.19 0.55 0.31 0.25 0.15

Tin 14.08 16.18 5.31 2.62 2.15 1.30 0.69 0.41 0.21 0.11

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Figure 4.4 to Figure 4.7 are drawn using the data of Table 4.5, plotting K/S values against wavelengths, which showed the similar trends in case of all the dyed fabrics.

Figure 4.4: K/S against wavelength curve of silk fabric dyed with henna extract

Figure 4.5: K/S against wavelength curve of silk fabric dyed with guava extract

0.00!2.00!4.00!6.00!8.00!10.00!

12.00!14.00!16.00!18.00!20.00!

K/S%

No!mordant!Ferrous!Sulfate!Ferrous!Sulfate!and!Alum!Ferrous!Sulfate,Alum!and!Tin!Alum!Alum!and!Tin!Tin!wavelength!

0.00!2.00!4.00!6.00!8.00!10.00!

12.00!14.00!16.00!18.00!

K/S%

No!mordant!Ferrous!Sulfate!"Ferrous!Sulfate!and!Alum"!Ferrous!Sulfate,Alum!and!Tin!Alum!Alum!and!Tin!Tin!wavelength!

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Figure 4.6: K/S against wavelength curve of silk fabric dyed with mango extract

Figure 4.7: K/S against wavelength curve of silk fabric dyed with onion extract

It was obvious that K/S values were increased by using mordants. Therefore it can be said that mordants increased the amount of dye absorbed by the fabric.

Ferrous sulphate has affinity for both the colourant and the fibre. This forms an insoluble complex with dye on substrate. When it was applied before dyeing, it enhanced the uptake of colourant. Tin and alum has more affinity towards dye compared to silk fibre. So tin and alum has a tendency to move out of the fabric into the dye bath during dyeing. Therefore the uptake was less when tin and alum was used as mordants. [10]

0.00!2.00!4.00!6.00!8.00!10.00!

12.00!14.00!16.00!18.00!20.00!

K/S%


0.00!2.00!4.00!6.00!8.00!10.00!

12.00!14.00!16.00!18.00!20.00!

K/S%


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4.4.2 Colour Co-ordinates of the samples

It was observed form the data in Table 4.6 that in all cases when ferrous sulphate mordant was used the DL* value was found least whereas when tin was used as mordant, DL* value was found maximum. Table 4.6 and Figure 4.8 revealed the trend that adding ferrous sulphate along with alum will decrease DL* value while adding tin with alum will increase DL* value. It can be concluded that in case of silk fabric dyed with henna, guava, mango and onion extract, ferrous sulphate mordants will produce darker shades while tin mordants will produce lighter shades.

Table 4.6: The colour co-ordinates of the mordanted silk fabrics dyed with natural

dyes

Veg. Dyes

Mordant

CIE Lab difference DL* Da* Db* DC* DH* ECIE

Henna Leaves

Ferrous Sulphate -21.55 -7.45 -11.44 -21.62 -3.23 25.51 Ferrous Sulphate and Alum -15.88 -4.60 -5.14 -10.79 4.55 17.31 Ferrous Sulphate, Alum and Tin -11.93 -2.13 -1.70 -6.85 3.20 12.24 Alum -10.41 0.00 2.04 0.90 5.20 10.61 Alum and Tin -8.17 0.90 3.86 3.76 4.82 9.08 Tin -5.50 1.32 4.82 1.64 5.25 7.43

Guava Leaves

Ferrous Sulphate -29.42 7.72 -20.45 -21.47 2.20 36.65 Ferrous Sulphate and Alum -11.69 7.60 -8.90 -6.57 2.09 16.54 Ferrous Sulphate, Alum and Tin -3.73 -5.32 -5.38 -2.45 1.20 8.44 Alum 1.40 -7.49 1.05 1.52 1.56 7.69 Alum and Tin 10.53 -3.40 5.08 3.86 0.86 12.18 Tin 12.72 -4.51 3.15 4.91 0.90 13.86

Mango Leaves

Ferrous Sulphate -42.77 0.20 -14.66 -14.33 -3.12 45.21 Ferrous Sulphate and Alum -35.12 0.55 -6.84 -6.84 -0.54 35.78 Ferrous Sulphate, Alum and Tin -12.80 -0.47 -2.59 -2.48 -0.89 13.07 Alum -10.27 -3.48 12.58 12.33 4.29 16.61 Alum and Tin -0.41 -1.03 3.18 3.03 1.40 3.37 Tin 0.82 -0.57 3.46 3.36 1.00 3.60

Onion Skin

Ferrous Sulphate -36.46 -7.54 -1.50 -4.23 6.43 37.26 Ferrous Sulphate and Alum -33.78 -7.34 1.53 -1.22 7.39 34.60 Ferrous Sulphate, Alum and Tin -22.13 -4.15 6.17 4.04 6.24 23.35 Alum -17.72 -2.74 16.84 14.72 8.62 24.60 Alum and Tin -10.23 2.93 14.39 14.18 3.80 17.90 Tin -9.40 5.20 10.06 11.31 0.56 14.72

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The DL* values displayed in Table 4.6 were shown through the following bar diagram in Figure 4.8.

Figure 4.8: Changes in L*(DL*) of mordanted silk fabric dyed with natural dyes

This higher DL* values and hence lighter shades of the fabric can be attributed to the fact that alum and tin forms quite strong bonds with dye but not with the fabric [10]. Thus it bleeds during dyeing from treated silk fabric and formed insoluble coloured complexes into dye bath. Ferrous sulphate has substantively for both the colourant and the fibre, this forms an insoluble complex with dye on substrate. When it was applied before dyeing, it enhanced the uptake of colourant and also formed complex which changed shade as well. Thus high concentration of ferrous sulphate gives deeper shades [10]. From the Table 4.6 it was found in case of all the dyes, tin and alum increased Db* val

Dyeing of Silk Using Vegetable Dyes and Study on the Effects of Mordants on the Dyeing Properties

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